Iminosugars and relatives as antiviral and potential anti-infective agents.

Iminosugars have emerged in the literature during mid-1960's as synthetic compounds. Around the same time, the first examples were found in Nature and their interesting enzyme inhibitory properties were recognised. Due to their powerful interference with glycohydrolases (glycosidases) as well as glycosyltransferases, quite a few representatives exhibit notable biological activities. These range from anti-diabetic, insect antifeedant, nematicidal, plant growth regulating to immunomodulating, anti-cancer as well as - in selected cases - anti-infective properties. The latter will be the focus of the following survey.

Powerful probes for glycosidases: novel, fluorescently tagged glycosidase inhibitors.

Amino-1,2,5-trideoxy-2,5-imino-D-mannitol was fluorescently tagged by reaction with dansyl chloride at N-1 or by attachment of a dansyl amide bearing spacer to this centre. Compounds obtained are highly potent inhibitors of beta-glucosidase exhibiting Ki values in the single figure nanomolar range. The 1-N-dansyl substituted inhibitor was successfully exploited for binding studies with beta-glucosidase from Agrobacterium sp. employing fluorescence spectrometric methods.

Ethambutol analogues as potential antimycobacterial agents.

A range of new ethambutol analogues was synthesised and their inhibitory potencies were probed with Mycobacterium smegmatis. Interestingly, apparently even minor deviation from the structure of the parent compound resulted in reduced antimycobacterial activity.

Novel, lipophilic derivatives of 2,5-dideoxy-2,5-imino-D-mannitol (DMDP) are powerful beta-glucosidase inhibitors.

Novel derivatives of the D-glucosidase inhibitor 2,5-dideoxy-2,5-imino-D-mannitol bearing lipophilic aliphatic or aromatic amides attached to C-1 have been found to inhibit beta-glucosidase from Agrobacterium sp. in the nanomolar range. One of them, a coumarin derivative, ranks amongst the most active compounds in the class of reversible glycosidase inhibitors of the iminoalditol type.

Syntheses of sugar-related trihydroxyazepanes from simple carbohydrates and their activities as reversible glycosidase inhibitors.

Five diastereomeric trideoxy-1,6-iminohexitols were synthesised, and their inhibitory activities were determined against selected glycosidases. For comparison, 1,4,5-trideoxy-1,5-imino-D-lyxo-hexitol, the 4-deoxy derivative of 1-deoxymannojirimicin, was prepared by enzymatic isomerisation of 6-azido-3,6-dideoxy-D-ribo-hexose into the corresponding 2-ulose and subsequent hydrogenation accompanied by intramolecular reductive amination.

Binding energy and specificity in the catalytic mechanism of yeast aldose reductases.

Derivatives of d-xylose and d-glucose, in which the hydroxy groups at C-5, and C-5 and C-6 were replaced by fluorine, hydrogen and azide, were synthesized and used as substrates of the NAD(P)H-dependent aldehyde reduction catalysed by aldose reductases isolated from the yeasts Candida tenuis, C. intermedia and Cryptococcus flavus. Steady-state kinetic analysis showed that, in comparison with the parent aldoses, the derivatives were reduced with up to 3000-fold increased catalytic efficiencies (k(cat)/K(m)), reflecting apparent substrate binding constants (K(m)) decreased to as little as 1/250 and, for d-glucose derivatives, up to 5.5-fold increased maximum initial rates (k(cat)). The effects on K(m) mirror the relative proportion of free aldehyde that is available in aqueous solution for binding to the binary complex enzyme-NAD(P)H. The effects on k(cat) reflect non-productive binding of the pyranose ring of sugars; this occurs preferentially with the NADPH-dependent enzymes. No transition-state stabilization energy seems to be derived from hydrogen-bonding interactions between enzyme-NAD(P)H and positions C-5 and C-6 of the aldose. In contrast, unfavourable interactions with the C-6 group are used together with non-productive binding to bring about specificity (6-10 kJ/mol) in a series of d-aldoses and to prevent the reaction with poor substrates such as d-glucose. Azide introduced at C-5 or C-6 destabilizes the transition state of reduction of the corresponding hydrogen-substituted aldoses by approx. 4-9 kJ/mol. The total transition state stabilization energy derived from hydrogen bonds between hydroxy groups of the substrate and enzyme-NAD(P)H is similar for all yeast aldose reductases (yALRs), at approx. 12-17 kJ/mol. Three out of four yALRs manage on only hydrophobic enzyme-substrate interactions to achieve optimal k(cat), whereas the NAD(P)H-dependent enzyme from C. intermedia requires additional, probably hydrogen-bonding, interactions with the substrate for efficient turnover.

Binding and catalysis by yeast aldose reductase: a substrate-analog approach with new aldose derivatives.

5-Deoxy-D-xylofuranose derivatives and a range of new 5,6-dideoxy analogs of D-glucofuranose bearing azido or fluoro substituents were synthesised and employed as substrates of the NADH-dependent aldehyde reduction catalysed by yeast aldose reductase. In terms of catalytic efficiencies, these products proved to be superior to the parent compounds.

A novel approach to the 1-deoxynojirimycin system: synthesis from sucrose of 2-acetamido-1, 2-dideoxynojirimycin, as well as some 2-N-modified derivatives.

6-Azido-1,3,4-tri-O-benzyl-6-deoxy-D-fructofuranose can be easily obtained in two steps from the known 6,6'-diazido-6,6'-dideoxysucrose (available in two steps from sucrose) and cyclized by controlled hydrogenation and concomitant intramolecular reductive amination to give 3,4,6-tri-O-benzyl-1,5-dideoxy-1,5-imino-D-mannitol, a partially protected derivative of 1-deoxymannojirimycin. After N-protection, position 2 is regio-specifically available to modification. This novel approach was taken advantage of in a synthesis of 2-acetamido-1,2- dideoxynojirimycin and new analogues thereof. Results of inhibition studies conducted with these new compounds employing N-acetylhexosaminidases of various sources are discussed.

A one-step C-linked disaccharide synthesis from carbohydrate allylsilanes and tri-O-acetyl-D-glucal.

The reaction of protected glucuronic esters 2 and 7, as well as D-glucuronolactone derivative 11, with (trimethylsilyl)methylmagnesium chloride in ether led to the corresponding stable bis-silyl adducts 3, 8, and 12, respectively. In Peterson-type reactions catalysed with mild acid, these compounds yielded carbohydrate allylsilanes 4, 9, and 13, respectively. Synthons 4 and 9 were coupled with tri-O-acetyl-D-glucal in a boron trifluoride-catalysed "carbon-Ferrier rearrangement" reaction to give C-linked disaccharides i.e., so-called "C-disaccharides" 16 and 17, respectively, in fair yields. Structural assignments of the anomeric configuration at the C-glycosylic carbon in the 2,3-unsaturated ring of these coupling products with the aid of n.m.r. spectroscopic methods unambiguously showed that alpha-D-C-linked disaccharides had been formed.